In the prior art, tanks used as reservoirs for storing fluids, such as gasoline, are generally installed underground. A typical example of such installation is the underground gasoline storage tank utilized at practically every automobile service station throughout the United States. Historically, such storage facilities have consisted essentially of large steel tanks buried beneath the concrete or asphalt surface of the service station. Steel tanks, however, tend to corrode after being buried for several years and must be repaired or replaced to avoid leakage and the resulting contamination of the surrounding ground and water supplies. During recent years, national attention has frequently been focused on the severe health hazards presented by underground fluid storage facilities which have failed to prevent their toxic contents from seeping into the surrounding earth and water. As a result, service station operators and others have sought economical ways of reducing the possibility of underground leakage and improving the ability to detect such leaks should they occur.
One conventional solution to the problems discussed above is the use of insulated or double walled tanks in conjunction with leak monitoring devices, such as the installation disclosed in U.S. Letters Pat. No. 4,110,947 issued on Sept. 5, 1978. Installations of this sort do an adequate job of detecting and containing leaks, but double walled tanks are very expensive and present some unusual installation problems. If the inner and outer walls of the double walled tank are both constructed of steel, for instance, the tank will be extremely heavy and difficult to maneuver into position. If, on the other hand, either or both walls are made of fiberglass, the tank will be comparatively light but it will also be delicate, so that the slightest bump during installation could cause undetectable damage to one or both walls. Additionally, regardless of whether they are steel or fiberglass, double walled tanks are larger than conventional tanks of the same capacity.
Another common solution to the leakage problems experienced with conventional tanks is the use of solid concrete vaults to encase the tanks. Vaults of this nature are typically rectangular in shape, with a floor and four walls constructed of reinforced concrete. The construction of such concrete vaults is laborious and time consuming, since forms must be placed along the walls and floor of the excavation and the concrete carefully poured into the forms and allowed to dry. Typically, freshly poured concrete vaults must cure for three or four days before the floor and walls are sturdy enough to allow the installation of the storage tank therein. In addition to the inordinate amount of time involved in building them, concrete vaults also experience frequent cracking problems, which would allow any leakage from the tank to enter the surrounding earth. In practice, concrete vaults have proven to be time consuming and generally unreliable devices for containing underground storage tanks.
Still another popular solution to underground leakage problems is the use of a leak-proof liner to surround the tank within the excavation. Typically, such liners consist of large plastic or vinyl sheets placed within the excavation prior to installing the tank. The most significant drawback with this technique is that the tank cannot be properly anchored without piercing the liner. The usual method of securing storage tanks in place includes the use of anchors either embedded in a concrete floor or retained by the gravel backfill. It is not feasible to employ such anchors with leak-proof liners, since an anchor protruding through the bottom of the liner would clearly destroy the liner's leak-proof characteristics. Additionally, the use of leak-proof liners requires that the walls of the excavation be shored or severely sloped to avoid cave-ins during installation; leak-proof liners are generally very flexible and do not provide any support for the earthen walls of the excavation. In consideration of the many problems associated with conventional underground storage tank installation methods, the present invention was developed to eliminate these problems.